Wire mat



W. D. ALLERS July 18, 1967 WIRE MAT 5 Sheets-Sheet 1 Filed April 15,1963 Juiy 18, w ERS 3,331,178

WIRE MAT Filed April 15, 1963 3 Sheets-Sheet 2 flaw m, W W Z y 5 w. 0.ALLERS 3,331,178

WIRE MAT Filed April 15, 1963 5 Sheets-Sheet 5 zgza .4 9 '73? Y (A p (A2/ Z4 r Z0 M 26 United States Patent 3,331,178 WIRE MAT William D.Allers, 105 W. Harris, La Grange, Ill. 60525 Filed Apr. 15, 1963, Ser.No. 273,227 9 Claims. (Cl. 52-660) This invention relates to a wire matparticularly suitable for use in prestressing concrete sheets and othermembers, and to the method of forming such a mat.

In Patent No. 3,084,910, issued Apr. 9, 1963, a method and apparatus aredisclosed for forming prestressed concrete sheets. An arrangement oftensors is provided for tensioning a plurality of wires over a bed, eachtensor in its preferred form comprising a horizontal rod carried by aplurality of arms or shoes which pivot at their ends about a horizontalpivot line parallel with but spaced from the axis of the rod. Apower-operated lever is connected to the tensor for slowly pivoting itto shift the horizontal rod downwardly and outwardly away from the bed,thereby stretching and tensioning the wires which are looped about therod and which span the bed. When the self-locking tensor is fullylowered and the wires have reached maximum predetermined tension, alayer of wet concrete is applied to the bed and, after the concrete hasfully hardened, the tensor is disconnected from the exposed ends of theimbcdded wires.

For effective stressing of the concrete sheet or other member, it isessential that the stretched and highly-tensioncd wires be securelyanchored within the concrete. Otherwise, the wires would contract assoon as they are cut or disconnected from the tensor and the concrete inwhich such wines are imbcdded would not be stressed. It is for thisreason, among others, that multiple strand twisted wire is preferred;the uneven contour of such wire plays an important part in achieving asecure interlock between that wire and the surrounding concrete.

Despite its important advantages, twisted wire has significantdisadvantages which makes it difiicult, expensive, and even dangerous touse in forming prcstressed concrete members. A particular problemconcerns the wide range and dangerously unpredictable level of maximumtension which such wire is capable of withstanding depending uponwhethcr it is tensioncd along a straight or curved line. Where the wirecurves sharply, as where it is looped around the horizontal rod of atensor, the different radii of curvatures for the various strands at anygiven point of contact with the tensor rod results in unequal stressingof the strands. The outermost strand at any given point is under greaterstress and tends to cut into the strand or strands in contact with thesurface of the tensor rod. Should one strand be severed by an adjacentstrand, a type of chain reaction occurs with many strands breaking,often at the same point, and the wire, with its tension suddenlyrelieved, lashing or whipping about. It should be noted that if anyslippage or relative movement occurs between the wire and the smoothsurface of the tensor rod during the tensioning step, such relativemovement significantly increases the possibility of the selfsevcringaction of the twisted wire.

Another problem relates to the diificulty of determining the stresslimits of twisted wire because of the slight strctchability whichinherently results from its twisted character. Even where such wire iscut into precisely equal lengths and each length is provided with itsown terminals on opposite sides of the bed, the variations in the stresslimits of each stretch of wire over the bed may give rise to breakageproblems. Where a single piece of twisted wire is strung back and forthover the bed to form an integral wire mat, the danger of breakage issubstantially greater because of the tendency of the various "icestretches to equalize their tension, and thereby slip over the smoothrounded surface of the tensor rod, as the tensor is shifted downwardlyinto its wire-tensioning position.

Accordingly, it is a principal object of the present invention toovercome the aforementioned defects and disadvantages in the wires andwire mats used in forming prestressed concrete members. Another objectis to provide a wire mat for use in forming prestressed concrete memberswhich has all of the important advantages of twisted wire without theabove-described disadvantages thereof. A further object is to provide amat of twisted wire which may be used in conjunction with theprestressing apparatus and method disclosed in the aforementionedcopending application without danger that one strand will tend to severanother against the outer surface of the tensor rod.

Another object of the present invention is to provide a one-piece wiremat which does not require reuse of conventional terminals and whichtherefore eliminates the disadvantages and problems inherent in the useof such terminals.

Other objects will appear from the specification and drawings in which:

FIGURE 1 is a broken top plan view of a bed and wire tensioningapparatus, the apparatus holding in fully tensioncd state a wire matembodying the present invention;

FIGURE 2 is a side clevational view of the bed, apparatus and mat shownin FIGURE 1;

FIGURE 3 is an enlarged broken perspective view illustrating in detailthe relationship between the tensor of the apparatus and the wire mat;

FIGURE 4 is a broken perspective view illustrating the structuraldetails of the mat;

FIGURE 5 is a perspective view of an apparatus for use in forming themat shown in FIGURE 4;

FIGURE 6 is an enlarged broken top plan view illustrating anintermediate step in the formation of the mat;

FIGURE 7 is a top plan view similar to FIGURE 6 but of reduced scale andillustrating a subsequent twisting step in the formation of the mat;

FIGURE 8 is a broken and somewhat diagrammatic plan view of a wire matprior to the twisting of adjacent stretches thereof;

FIGURE 9 illustrates one way in which the wire shown in FIGURE 8 may betwisted to form a completed mat;

FIGURE 10 illustrates a second way in which the wire of FIGURE 8 may betwisted to form a completed mat;

FIGURE 11 illustrates a third way in which the wire of FIGURE 8 may betwisted to form a completed mat.

Referring to FIGURES 1-ll of the drawings, the numeral 10 generallydesignates a mat which embodies the present invention and which isformed from a single piece of wire or other filament. The word "wire" ishere used to mean a filament formed of metal or any other materialhaving the requisite characteristics of strength and durability. Whilein most instances the wire is preferably formed of steel or othersuitable metal, it is to be understood that the "wire" may alternativelybe formed of nylon or other plastics.

In FIGURES l, 2 and 3 the mat is shown in use in conjunction with a bedA and tensor 8 of the type generally disclosed in Patent No. 3,084,910to which reference has previously been made. The bed consistsessentially of a slab 11 having a top surface 12 in the shape of aconcrete member 13 to be formed thereon. In the illustration given,surface 12 is fiat and member 13 constitutes a thin concrete sheet. Onopposite sides of the bed are upstanding posts 14 and 15. Posts 14 bearagainst one side of slab 11 and brace the foundation 16 as well as thehorizontal rod 17 which is held tightly against the posts by the highlytensioned wires looped thereabout.

The series of spaced upstanding posts 15 along the opposite side of theslab are interposed between that slab and an inclined platform 18. Theplatform is horizontally elongated and slants transversely upwardlytowards the series of postslS to provide an inclined supporting surfacefor tensor B.

The tensor consists essentially of a horizontal rod 19 which isrotatably supported in the end matches 20 of a plurality of inwardlyextending pivot arms or shoes 21. All of the spaced parallel arms arerigidly interconnected by a connecting bar 22 and the inner ends of thearms are rounded (in vertical planes) and bear against posts 15 andplatform 18. Thus, the tensor B is capable of pivoting about a pivotline parallel with and spaced inwardly with respect to the axis oftensor rod 19, the range of pivotal movement being represented in FIG-URESZ and 3 by the raised position of FIGURE 3 (also shown in brokenlines in FIGURE 2) and the lowered position of FIGURE 2.

When the tensor is in its fully lowered position, the axis of rod 19 isspaced below the pivot line of the tensor and the tension of thestretched wire mat effectively locks the tensor in place. During thewire-tensioning operation, as the tensor is pivoted downwardly, rod 19is free to rotate about its own axis and within the notches 20 of thepivot arms, thereby eliminating or reducing slipping contact between thewire and the rod. Downward pivoting movement of the tensor is mosteasily accomplished by connecting a suitable lever extension (not shown)to the tensor to increase the mechanical advantage of the applied force.Such a lever assembly and a form of winch used in connection with itsoperation are fully disclosed in the aforesaid copending applicationand, since they form no part of the present invention, need not bedescribed in detail herein.

Mat consists of a single strand of wire which extends between thestationary horizontal rod 17 and tensor rod '19. With the exception ofthe terminal stretches, all of the stretches of wire which extend backand forth between the stationary rod and the tensor rod are ofsubstantially identical length. Since the rod 17 extends along the samehorizontal plane as the uppermost edge portion of platform 18, thestretches of fully tensioncd wire extend in the same horizontal planebetween spaced points along a pair of spaced parallel lines.

Referring to FIGURES 4, 9 and 1, it will be observed that adjacentstretches of the wire have their intermediate portions twisted togetherto provide a plurality of parallel double-strand intermediate sections23. At one end of each intermediate section is a single-strand loop 24which, in the illustrations given, is fitted over stationary rod 17. Atthe opposite ends of the intermediate sections (and along the oppositeside of the mat) are a plurality of single-strand loops 25 whichinterconnect adjacent intermediate sections of the mat. In contrast tobridging loops 25, each of the loops 24 is closed and extends to only asingle intermediate section.

The terminal stretch of wire 26 returns to the terminal intennediatesection 27 so that such section differs from the other intermediatesections 23 in being formed of three strands twisted together. As aresult of such construction, closed loops 24 and 28 are provided atopposite ends of each terminal intermediate section 27. The extreme endof terminal stretch 26 may be affixed to the remaining strands of theintermediate portion 27 by any suitable connecting means; however, ithas been found that if the mat is of sufficient size and the terminalintermediate portlon 27 is suflicicntly twisted, no additionalconnection between the three strands of the section 27 is required.

Each of the two-strand intermediate sections 23 has an identical numberof twists. The terminal intermediate portions 27 may have one or morefewer twists to compensate for their greater thickness. The result is amat having a plurality of integral elements (each element consisting ofend and intermediate sections) of substantially identical overall ortotal length.

The mat 10 is formed from a single strand of wire by the methodillustrated in FIGURE 5 through 7. The single-strand wire iscommercially available on large spools and, as a preliminary step in theformation of the mat, the wire 29 is unwound from the spool (not shown)ont reel 30. The reel may be generally H-shaped composed of a pluralityof interconnected side, end, and intermediate members 31, 32, and 33,respectively. The reel is rotatably mounted upon a horizontal shaft 34which passes through the centers of intermediate members 33, therebyfacilitating the winding of the wire 29 under generally uniform tensionupon the reel. End members 32 are all parallel with each other and arepreferably provided with a series of spaced-apart arcuate recesses 35,each of the recesses being adapted for slidably supporting only a singlecoil of the wire 29 wrapped about the reel. The wire is wound about thespool with a degree of resistance sufiicient to place equal lengths ofwire about each turn of the reel.

After the wire is fully wound upon the reel but has not been severedfrom the supply spool, two series of pulleys 36 and 37 are brought intocontact with the inner surfaces of the coils of wire as shown in FlGURE5. The two sets of pulleys 36 and 37 are rotatable about axes which areparallel with each other and with the end members 32 of the reel. Eachpulley is independently rotatable about its own axis, and at least oneof the sets is constructed so that the pulleys thereof may also berotated about the axes of their mountings. In the illustration given,the pulleys of set 36 are independently rotatable about the axle 39 ofindividual mounting elements 40, although it is to be understood (forreasons which will appear hereinafter) that the pulleys of set 37 may besimilarly mounted, rather than being mounted upon a single shaft 38. Itwill also be noted that the spacing between the pulleys of each setcorresponds with the spacing between the recesses 35 of each end member32. Therefore, as the two sets of pulleys are drawn outwardly inopposite directions, the groove of each pulley receives a portion of asingle coil of the wire 29 wound about the reel 30.

The particular carriage means used to support each set of pulleys foroutward movement with respect to the reel may vary considerablydepending upon the size, location and capacity of the particularinstallation. Whatever the design of the particular carriage means, itis essential in forming a rectangular mat that the axes of the two setsof pulleys remain at all times in parallel relation with each other.Since the wire 29 remains connected to the supply spool (not shown). andsince the wire is freely slidable within the recesses 35 of end members32, outward movement of the two sets of rollers produces longitudinalsliding movement of the wire 29 about the reel. Additional wire, as itis required, is provided by the supply spool. Outward movement of thepulleys is continued until the stretches of wire extending back andforth between the parallel rolls of pulleys are of a preselected length.The wire is severed from the supply spool and, with opposite ends of thewire entrained about the pulleys anchored securely in place, apredetermined outward force is applied to the two sets of pulleys 36 and37 to produce uniform tension in all of the stretches 29 ohvire.

Where only a relatively small mat is desired, the wire may be wound uponthe reel in uniformly tensioned condition, and thereafter removed fromthe reel, by disassembling, partially collapsing, or otherwise reducingthe size of the reel, for placement of the wire upon an arrangement ofopposing pulleys.

Thereafter, each of the pulleys -35 is rotated about a radial axisgenerally parallel with the stretches of wire extending therefrom(FIGURE 7). The pulleys 36, with the possible exception of terminalpulleys 36a, are rotated an identical number of turns in the same ordifferent direction. The terminal pulleys 36a may be rotated one or morefewer turns in the same or diiierent direction because of the fact thatthe terminal intermediate sections 27 comprises three strands of wirerather than only two strands as in intermediate sections 23. When thewire is fully twisted, the looped end sections 24, 25 and 23 are removedfrom the pulleys. The results is a mat formed of wire having generallyparallel elements of equal length, each element consisting of a doublestrand intermediate section (except for the terminal elements) andsingle strand end sections.

Since the end sections are only of single strand construction, they maybe looped about the horizontal movable tensor rod 19, or the stationaryvertical tensor rods 17, of the apparatus illustrated in FIGURE 1, andthe wire elements of the mat may then be stressed or stretched withoutdanger that one strand might sever another strand in contact with thetensor rods. Furthermore, since the elements of the mat are of identicallength, with all of the two-strand intermediate portions having anidentical number of turns or twists, there is no appreciablelongitudinal sliding movement of the wire over the tensor rods during atensioning operation. These important results are achieved while at thesame time providing a mat having wire elements with twisted intermediatesections. Such sections constitute the principal length of each Wireelement and are essentially the only sections imbedded in the concretemember formed thereabout. Therefore, because of the twisted character ofthe imbedded wire, the chances of wire slippage in the finished concreteproduct are substantially eliminated.

FIGURES 8 through 11 illustrate diiferent ways in which the same wire,previously stretched and preformed by the means illustrated in FIGURESand 6, may be twisted to form mats of different configuration. Startingwith the wire with parallel stretches 29 as illustrated in FIGURE 8, thelooped ends designated by the letters A, B and C may be rotated bypulleys 36 in the manner already described to form the completed matIll) (FIG- URE 9) in which A, B and C become closed loops 24. Loops D-G,supported by pulleys 37 all carried upon the same shaft 38, form openloops 25 and closed loop 23 in the final mat ill.

The same wire or" FIGURE 8 may be twisted different- 1y to form themodified mat 11) illustrated in FIGURE 19. Mat ill is formed bysuperimposing loops D and E, and twisting them simultaneously whileholding loops A, B and C stationary. Loops F and G are separatelytwisted in the same manner as composite loops D, E. As in mat 1d, theintermediate portions 23' of mat it) are twisted the same number ofturns, whereas the terminal intermediate portion 27 has a lesser numberof turns to form twisted elements of equal length. One advantage of mati over mat ill lies in a more secure connection between the terminalstretch 26' and the remaining wire portions which form the terminalelement.

The mat ii)" of FIGURE ll is similar to the mat 19' of FIGURE exceptthat the pulleys supporting loops A, B and C have been rotated as wellas the pulleys supporting loops D-E, F and G. In other words, mat lit)is formed by twisting the wire of FIGURE 8 from all of the looped ends,the apparatus for periorming such an operation consisting, as alreadyindicated, of opposing sets of independently mounted pulleys 36.

From the foregoing, it is believed apparent that mats having singlestrand looped end portions and twisted intermediate elements may assumea variety of configurations. All of the elements of such mats are ofsubstantialy identical length and, therefore, there is no appreciablelongitudinal sliding movement of the wire over the tensor rods during atensioning operation. Since the portion of the mat embedded in theconcrete consists primarily of twisted wire, the mat is firmly anchoredin place and is well able to perform its essential function inprestressing the surrounding concrete body.

While several embodiments have been disclosed in considerable detail forpurposes of illustration, it will be understood by those skilled in theart that many of these details may be varied without departing from thespirit and scope of the invention.

1 claim:

1. A pre-formed wire mat for use in prestressing concrete memberscomprising a strand of wire extending between spaced points along a pairof spaced parallel lines to define a plurality of stretches of wire ofsubstantially identical length, adjacent stretches of said wire havingintermediate portions thereof twisted together to provide a plurality ofparallel double-strand intermediate sections, all of the double-strandintermediate sections of said mat having an identical number of twists,each of said intermediate sections having the twists thereof extendingin the same rotative direction and comprising an identical number oftwists of each of the wires forming such section, said mat including endsections at opposite ends of said intermediate sections, saidendsections consisting of single-strand loops adapted to, receive tensorrods for the stressing of said wire mat, the loops along one side ofsaid mat interconnecting adjacent double-strand intermediate sections ofthe mat.

2. The structure of claim 1 in which each of the loops at the oppositeside of said mat is closed and extends to only a single double-strandintermediate section.

3. A pre-formed wire mat for use in prestressing concrete members, saidmat comprising a plurality of generally parallel wire elements extendingfrom one side to the other side thereof, each of said elements having amultiple-strand intermediate section and single-strand loops at oppositeends thereof, the strands of each of said elements being ofsubstantially identical length, the loop at one end of each elementbeing closed and a loop at the opposite end thereof being open andconnecting the intermediate sections of adjacent elements, saidsinglestrand loops being adapted to receive tensor rods for thestressing of the elements of said wire mat, each multiplestrandintermediate section being twisted and having the twists thereof allextending in the same rotative direction and composed of an identicalnumber of twists of each of the strands of such section.

4. The structure of claim 3 in which all of said elements excluding theterminal elements of said mat have double-strand intermediate sections.

5. The structure of claim 4 in which said multiplestrand intermediatesections all have identical numbers of twists.

6. The structure of claim 4 in which the terminal elements of said matare provided with intermediate sections each having a greater number ofstrands of wire twisted together than the intermediate sections of theother remaining elements, the number of twists of intermediate sectionsof each of said terminal elements being no greater than the number oftwists of each of said other elements.

7. A pre-formed wire mat for use in prestressing concrete members, saidmat being formed from a single piece of single-strand wire andcomprising a plurality of generally parallel wire elements extendingfrom one side to the other side thereof, each of said elements havingmultiple-strand intermediate sections and single-strand loops atopposite ends thereof, the strands of each of said elements being ofsubstantially identical length, the intermediate sections of all of saidelements other than the terminal elements of said mat consisting oftwisted double strands of wire having identical number of twists, theloop at one end of each element of said mat being closed 7 and a loop atthe opposite end thereof being open and connecting the intermediatesections of adjacent elements, said single-strand loops being adapted toreceive tensor rods for the stressing of the elements of said wire mat,each multiple-strand intermediate section having the twists thereof allextending in the same rotative direction and composed of an identicalnumber of twists of each of the strands of such section.

8. The structure of claim 7 in which the terminal elements of said matare each provided with intermediate sections having at least threestrands of wire twisted together.

9. The structure of claim 7 in which all of the elements of said mat areof substantially identical length.

References Cited UNITED STATES PATENTS 656,024 8/1900 Kemnitz' 50-136659,416 10/1900 Perry 50495 907,024 12/1908 Flagg 50-143 1,661,6423/1928 Voight 50495 1,692,166 11/1928 Gates 25-131 3,025,890 3/1962 Clay14071 3,125,132 3/1964 Knisely 14071 DAVID J. WILLIAMOWSKY, PrimaryExaminer.

REINALDO, P. MACHADO, HARRISON R. MOSE LEY, KENNETH DOWNEY, Examiners.

1. A PRE-FORMED WIRE MAT FOR USE IN PRESTRESSING CONCRETE MEMBERSCOMPRISING A STRAND OF WIRE EXTENDING BETWEEN SPACED POINTS ALONG A PAIROF SPACED PARALLEL LINES TO DEFINE A PLURALITY OF STRETCHES OF WIRE OFSUBSTANTIALLY IDENTICAL LENGTH, ADJACENT STRETCHES OF SAID WIRE HAVINGINTERMEDIATE PORTIONS THEREOF TWISTED TOGETHER TO PROVIDE A PLURALITY OFPARALLEL DOUBLE-STRAND INTERMEDIATE SECTIONS, ALL OF THE DOUBLE-STRANDINTERMEDIATE SECTIONS OF SAID MAT HAVING AN IDENTICAL NUMBER OF TWISTS,EACH OF SAID INTERMEDIATE SECTIONS HAVING THE TWISTS THEREOF EXTENDINGIN THE SAME ROTATIVE DIRECTION AND COMPRISING AN IDENTICAL NUMBER OFTWISTS OF EACH OF THE WIRES FORMING SUCH